The present invention relates to a forming press of crankshafts.
A one-piece crankshaft is forged in stages of closed die forging, twisting, and reshaping. Although the stage of closed die forging consists of the substages of preforming, rough closed die forging, finishing closed die forging, and trimming, all the four substages are being performed with a single forging press since it is required in all the four substages to apply pressure to the workpiece in only the downward direction. On the other hand, because the twisting stage and the reshaping stage require different pressing modes, the two stages were being performed with two different forging presses. However, because using two different forging presses for the two stages is disadvantageous in terms of equipment cost and man-hours, forming presses have recently been developed which, in a single unit, are capable of performing both the twisting and reshaping stages. The present invention relates to such a forming press.
A forming press of crankshafts is disclosed in the Japanese Examined Patent Publication No. 4640/H7 (1995), which is shown in FIG. 25.
In the above forming press, a slide 106 is secured to the lower ends of the piston rods of piston cylinders 108, which are mounted on the crown. An upper die holder 151 is secured to the bottom of the slide 106. The upper section of a twisting die 101 and the upper section of a reshaping die 102 are fixed to the bottom of the upper die holder 151. On the other hand, the lower sections of the twisting die 101 and the reshaping die 102 are mounted on a lower die holder 152, which is mounted on the base of the forming press. The twisting die 101 and the reshaping die 102 are built in so that the upper and lower sections of the twisting die 101 and those of the reshaping die 102 join at one and the same height when the slide 106 comes down. When the slide 106 descends, a workpiece is caught between the upper and lower sections of the twisting die 101 and, at the same time, another workpiece in the reshaping die is pressed and reshaped. While the slide 106 is in its bottom position, the twisting oil-hydraulic cylinder 109 provided in the slide 106 contracts to lower push rods 171 penetrating the slide 106 and twist the workpiece in the twisting die 101.
In this way, a workpiece can be reshaped in the reshaping die 102 and, at the same time, another workpiece can be caught between the upper and lower sections of the twisting die 101. Then, the workpiece in the twisting die 101 can be twisted by contracting the twisting oil-hydraulic cylinder 109, pushing down the push rods 171, and thereby turning parts of the twisting die 101 anticlockwise and the other parts of the twisting die 101 clockwise.
In case of the above forming press, because the twisting oil-hydraulic cylinder 109 is disposed in the slide 106, it is necessary for feeding hydraulic oil to the twisting oil -hydraulic cylinder 109 to use long flexible hoses 100 which cover the stroke of the slide 106. Such configuration is not desirable for a high-speed production machine which requires a large flow of hydraulic oil, posing a large danger of hydraulic oil leaking from the long flexible hoses 100, igniting from the heat of the hot forging, and causing a fire.
Besides, to bring the lower ends of the push rods 171 to the push-down arms 104 of movable retainers holding the twisting die 101, the slide 106 has to allow the push rods 171 to penetrate itself. In this configuration, the following shortcomings occur.
(1) The adjustment and maintenance of the guiding parts of the push rods are difficult. PA0 (2) Because the slide 106 is divided into three by the push rods 171, its strength is reduced. To solve this problem, the height of the slide 106 has to be increased to recover its strength. PA0 (3) Accordingly, the slide system (moving section) becomes heavy. Its large force of inertia impedes the control of high-speed cyclic operation.
One of the main objects of developing a forming press which performs both the twisting and reshaping stages is to achieve a high-speed operation. In case of the above forming press of the prior art, the object is difficult to achieve due to the reasons described in the above paragraphs (2) and (3). If the forming press achieves the object, it would present problems in forming precision and maintenance.
On the other hand, the twisting angle of such a forming press has to be changed in accordance with the types of crankshafts. The twisting angle varies depending on the numbers of cylinders, etc. of engines.
In conventional means for setting the twisting angle, stoppers are set, below the push rods, on the top of the bed to regulate the twisting angle. To shift the production from one type of crankshaft to another, stoppers have to be changed and adjusted to attain the twisting angle required by the latter.
Such stoppers have to be changed and adjusted by workers in accordance with twisting angles required by various types of crankshafts. Besides, because the space in the forming press is limited, the upper and lower die holders are usually taken out of the press in order to make fine adjustment of the stoppers. Accordingly, working efficiency is low.
Under the circumstances, another forming press is disclosed [Japanese Unexamined Utility Model Publication 104215/H4 (1992)]. The forming press has, under its bed, a driving mechanism which moves threaded shafts up and down to adjust the height of the stoppers.
However, because the driving mechanism is disposed under the bed, die lubricant and scale stick to the driving mechanism and hence it is liable to develop trouble. Besides, because the forming press has four stoppers, they require fine height adjustment among them. Therefore, the driving mechanism for adjusting the height of stoppers is very complex and expensive.
In accordance with the above, an object of the present invention is to provide a forming press of crankshafts of which the safety is high, of which the slide has large strength ensuring high precision, and which is capable of high-speed operation and inexpensive.
Another object of the present invention is to provide a forming press of crankshafts of which the twisting angle can be set freely and precisely, of which the construction is simple, and which is inexpensive to make and is capable of high-precision forming.